1. Field of the Invention
This invention relates generally to penile prostheses and more specifically to parylene-coated components used therefor.
2. Description of the Related Art
The implantation of a penile prosthesis is one known treatment for the condition in human males known as erectile dysfunction or ED. Once implanted, the penile prosthesis is used to artificially create an erection, thus allowing the patient to be sexually active.
Such prosthesis generally includes a pair of inflatable cylinders which are implanted, in parallel, in the patient's corpus cavernosae. The prosthetic also includes a pressurized reservoir of fluid that is implanted elsewhere in the patient's body, usually in the abdomen. A pump and valve assembly is fluidly coupled to the reservoir via reservoir tubing and the pair of inflatable cylinders are then fluidly coupled, via fluid passageways, to the pump and valve assembly. Upon actuation of the pump and valve assembly, the cylinders become pressurized due to fluid transfer from the reservoir to the pump and valve assembly and from the pump/valve to the cylinders which, in turn, causes the cylinders to become rigid. This rigidity thereby causes the desired erection.
There are several variations of such a prosthetic. For example, the cylindrical members can expand as they are pressurized, or in another variation, they may simply go from an empty, flaccid state to a full, rigid state, with no expansion of the cylinder(s). The reservoir and/or the pump assembly can also be made integral with the cylinder(s).
In order to adapt the prosthetic to the patient's anatomy, the cylinders have arcuate front and rear cap portions which mate well with the ends of the corpus cavernosae. Moreover, the caps serve to form a sealed chamber within the cylinder thus enabling the cylinder to inflate.
In order to control the expansion of the cylinder as it is inflated, a sleeve of fabric or other cloth-like material is placed around an inner tube of the cylinder. Thus, the diameter of the cylinder can only expand to a size congruent with the fabric sleeve. The use of a fabric sleeve also effectuates a uniform inflation. Typically, a second sealed outer tube is placed around the inner tube and the fabric sleeve. Thus, a typical cylinder wall includes two tubes, one within the other. Consequently, proper functioning is dependent on the correct operation of the inner tube and, in some embodiments, on the correct operation of the outer tuber as well. That is, in some cases, the area around the outer tube is used for fluid transfer and/or storage. A fabric sleeve may also be used with those types of cylinders that do not expand when filled, but simply become rigid.
The double walled structure is an efficient arrangement. One potential issue is the continuous contact between each of the tubes and the fabric. The prosthetic exists in a relaxed or flaccid state a majority of the time and thus the inner and outer tubes are in contact with the fabric a majority of the time. The specifics of this situation are elaborated below.
In order to provide comfort and a better sense of normalcy to the patient, the prosthetic is made from materials that allow the prosthetic to bend and be flexible when in the flaccid state. Such bending, however, may lead to the formation of a crease in the walls of the double-walled or single-walled device. This crease terminates in bend corners that are areas of stress and highly localized areas of contact between the cylinder's inner and outer tubes and the fabric sleeve. Consequently, as the flaccid cylinder is bent from side to side or generally moved about a central axis due to normal movement of the patient, the bend corners will likewise travel thus resulting in pockets of the cylinder contacting and moving across each other. This results in a movement of the corners which causes portions of the tubes to contact (and move across) each other. There is also a potential element of material fatigue as the various materials are repeatedly stressed and unstressed.
Moreover, since the crease generally occurs in the same location on the cylinder, the same areas of contact are repeatedly moved across each other. Over time, this repeated contact and movement may lead to wear, abrasion, and fatigue.
Typically, the tubes are formed from a versatile material such as silicone or polyurethane which are medically safe and provides the necessary degree of structural reliability. It has been found that silicone has a high coefficient of friction and can be somewhat tacky. As a result, when silicone contacts itself or some other surface, it can bind and resist movement. Indeed, this frictional engagement could cause the contacting surfaces to wear at these contacting locations and eventually could potentially cause the tubing to wear and fatigue.
For the same reasons, similar situations may be encountered with other components of the prosthesis. The fluid passageways, the reservoir, the housing for the pump and valve assembly are all typically made from silicone. Thus, in any instance where the silicone surfaces of these components are caused to bend, to contact other silicone surfaces, or to fatigue, similar situations of wear may be encountered.